A. Field of the Invention
This invention relates generally to the field of surgery, and in particular relates to techniques for aligning a surgical drill with transverse holes of an intramedullary nail which has been implanted in long bones of a patient.
B. Description of Related Art
In repairing broken bones, and particularly long bones of the body such as the humerus, femur or tibia, a common surgical practice is to insert a hollow tubular part known as an intramedullary nail into the interior portion of the bone. The intramedullary nail is then secured in place with respect to the bone by installing one or more transversely-extending screws or bolts at the proximal and distal portions of the intramedullary nail. The intramedullary nail serves to enhance the healing of the broken bone by providing a rigid structure about which the broken portions of the bone may adhere.
In order to install the screws or bolts in the intramedullary nail and bone, a screw hole must be drilled transverse to the bone in direct alignment with each transverse hole in the intramedullary nail. This drilling is performed after the intramedullary nail has been inserted into the bone canal. It is desirable that drilling should pass cleanly through the transverse holes, to prevent metal shreds and shavings from being formed when the drill touches the nail. Such shavings may impede healing, and may cause post-operation discomfort or pain for the patient. Further, if the hole was not properly drilled, a second or even a third through hole may have to be drilled, weakening the bone and delaying the healing process. It is not possible to see the transverse holes directly, since the intramedullary nail is disposed inside the bone canal. An arrangement must be provided for the alignment of the surgical drill with the transverse hole through the intramedullary nail.
Several approaches have been used to determine the location of the transverse holes to provide the necessary alignment of the drill with the hole during the drilling process. The approaches utilize conventional X-rays, in a majority of the time, or magnetic sources and sensor arrangements. The X-ray approach exposes the surgeon, the patient, and other personnel to a certain degree of irradiation for a relatively long period of time, which is a health concern. A recent approach to reduce long X-ray exposure during the procedure uses a laser light source coupled to an X-ray image intensifier. After alignment of the drill with the aid of an X-ray machine, the unit is turned off and a laser light spot is used to mark the location of the hole on the surface of the patient's extremity. The laser spot provides a starting location for drilling from the outside, but it does not provide visual alignment to the transverse hole inside the patient's extremity. Moreover, the surgeon's hand and drill get in the way of the laser.
The magnetic source and sensor approach provides a magnetic source or sensor inside and outside the patient and uses the magnetic field intensity as a function of position as the indicator of alignment. These magnetic source/sensor arrangements provide imprecise and cumbersome alignment either due to the magnetic source's relatively uniform maximum field strength in the region of maximum field, or the necessity of interpreting visual indicators providing the location of the magnetic sources and coordinating drilling movements with the indicators.
The use of magnets in aligning a surgical drill with the transverse holes of an intramedullary nail is described in the Thomas patent, U.S. Pat. No. 5,127,913. The problem of aligning an intramedullary nail with transverse anchoring members is also discussed in the patent to Klaue, U.S. Pat. No. 4,817,591, the patent to Taylor, U.S. Pat. No. 4,667,664, the patent to Brudermann, U.S. Pat. No. 4,621,628, and Canadian Patent Application 2,073,266, entitled Distal Targeting System.
These efforts to solve the problem of accurate alignment of the surgical drill and the transverse holes of the intramedullary nail have achieved limited success, and only marginal acceptance by orthopedic surgeons. They also typically rely on expensive and cumbersome equipment. The methods that involve X-ray and image intensifier equipment also involve the display of bone and intramedullary nail images remote from the area of interest, such that the surgeon must look away from the patient to a screen to see if he or she is drilling in the proper location. This adds additional inconvenience to the surgeon. In actual practice, a free hand method of determining the location of the transverse holes is still often used, but this technique has its own inherent limitations and inaccuracies. Because of these shortcomings in the aforementioned techniques, the use of intramedullary nails as a treatment modality is much less frequent than it would otherwise be if a simple, safe, and accurate distal targeting technique were available to surgeons. The optical distal targeting system of the present invention overcomes these shortcomings of the prior art and provides a safe, relatively inexpensive, easy to use, and accurate means for locating transverse distal and proximal holes of an intramedullary nail.